An electrical or power substation involves electricity transmission and distribution systems where voltage is transformed from high to low or the reverse using transformers. Electric power may flow through several substations between generating plant and consumer, and may be changed in voltage in several steps.
The substations can include one or more transformers, and switching, protection, control, metering and grounding equipment. Appropriate equipments are selected for these functions depending on whether the substation is a transmission, sub-transmission, or distribution substation. Currently different types of Intelligent Electronic Devices (IEDs) are used in the substation to cater to different substation functions. The IEDs are microprocessor-based controllers of power system equipment, such as circuit breakers, generators, transformers, power lines, power cables, reactors, motors, capacitor banks etc. For example, the IEDs receive data from sensors and power equipment, and can issue control commands, such as tripping circuit breakers if they sense voltage, current, or frequency anomalies, or raise/lower voltage levels in order to maintain the desired level. Known types of IEDs include protective relaying devices, load tap changer controllers, circuit breaker controllers, recloser controllers, voltage regulators, etc. With the available microprocessor technology, a single unit can perform several protection, metering, monitoring and control functions concurrently.
Substation automation can be an important and complex aspect for maintenance and control of different equipments involved in different processes within the substation. Multiple protocols exist for substation automation, which include many proprietary protocols with custom communication links. However, interoperation of devices from different vendors can be highly desired for simplicity in implementation and use of substation automation devices.
The IEC61850 standard from International Electrotechnical Commission (IEC) advocates interoperability amongst Intelligent Electronic Devices (IEDs) from various manufacturers using common engineering models, data formats and communication protocol. Recent IEDs are therefore designed to support the IEC61850 standard for substation automation, which provides interoperability and advanced communications capabilities.
IEC 61850 features include data modeling where complete functionality of the substation is modeled into various IEC61850 compliant logical nodes that are grouped and arranged under different logical devices. Logical nodes are the smallest part of a function that exchanges data and these logical nodes are objects defined by its data and methods. Logical devices are virtual devices that exist to enable aggregation of logical nodes and data sets for communication purposes.
There are logical nodes for data/functions related to the logical device (LD) and physical device (LPHD). The data can emanate from an IED through various schemes like GOOSE (Generic Object Oriented Substation Events) events, reports, Sampled and Measured Values (SMVs). An IED can receive the commands from a client or peer IEC 61850 system. Regarding data storage, a SCL (Substation Configuration Language) is defined for complete storage of configured data of the substation in a specific format.
The abstract data models defined in IEC61850 can be mapped to a number of protocols. Current mappings in the standard are to MMS (Manufacturing Message Specification), GOOSE (Generic Object Oriented Substation Event), SMV (Sample Measured Values), and soon to Web Services. These protocols can run over TCP/IP networks and/or substation LANs (local area networks) using high speed switched ethernet to obtain desired response times of less than four minutes for protective relaying.
The IEC61850 standard also makes provision for addressing of data within an IED that is generally, addressed by respective IED engineering/configuration tools. The addressing concepts are adapted to suit the philosophies that are applicable for any internal variables' data being communicated between the IED's hardware components.
The IEC61850 standard supports two different attributes for addressing, depending on whether data emanates from the IED or in other words is published from the IED, using GOOSE/SMV/MMS profile or whether the IED receives data from other peer IEDs, using the GOOSE/MMS communication profiles. The information terminating into the IED via GOOSE should be flexible as one may not know the number of signals being subscribed by the IED from other peer IEDs a priori, when the IED engineering is started.
For IEDs that support a predefined or fixed super set of configurations, the internal addressing can be generally constant. The IED tool, based on the selected configuration, generates the desired ICD/CID file (IED configuration description file/Configured IED Description file) for publishing information. However, for IEDs like Process Controllers or ‘Intelligent’ Remote I/O systems or ‘I/O configurable’ Protection and Control relays, that allow partial or completely flexible arbitrary configurations, a constant addressing scheme can limit the functionality. Unless the address scheme is a flexible one, the information that is to be published from the mentioned IED types (Process Controllers or ‘Intelligent’ Remote I/O systems or ‘I/O configurable’ Protection and Control relays) to other recipient IEDs may not be unique.
Hence, the present disclosure presents a flexible addressing technique that utilizes the ability of IEDs to be configured as per a user or substation specification.